Some first testshots pop up on the world-wide-wibble:
http://www.pbase.com/miljenko/s150_500vs50_500Comparison against the Sigma 50-500mm done on a Canon 20D.
The lens is available in Germany for Canon but not yet for Nikon.
(Pre-)order for around 850€ (incl. 19% you-know-VAT).

I will be using on the Nikon D300 and already have the Nik18-200m. Interested in the Sig lenses for the 500m reach for wildlife. I have looked through the forums at Alex Venom's photo reviews of the 150-500 and kpr's input of the 50-500m. Difference in pricing is not a detail that concerns me if the quality is better. I don't plan on using the teleconverter for either lens. Help and input greatly appreciated.

Hmmm, Jim. This is a tough one!
I have not seen anybody compare both lenses under equal conditions. But perhaps someone in our readership has???
I'd suppose that the 150-500 is the better lens, because:
- more recent design
- smaller zoom-range is easier to design/correct
But this is just an assumption, mind you!

Thanks Thomas. I just don't see much difference in the comparison photos that were linked in your first post. I would suppose the EX build would be better glass, but then the OS on the 150-500m would be very beneficial at the long range. And price is usually an additional indicator of glass quality. Users of either lens rate them highly so I guess the 150-500 w/ OS fits my needs better, given that my 18-200 covers the lower range.

Knowing then what I know now,
I would have chosen the 150- instead of thinking going down to 50mm might be benificial by times.
It has saved me changing lenses a few tmes.
Great lens Rebel, I don't think you'll be disappointed.

We just purchased this lens and are really impressed with the image quallity and the speed of the autofocus i even took a few indoor shots of our daughter with the lens and was very impressed with its low light capabilities. and the OS works very well . we thought we would be compromizing by buying 3rd party equipment but so far the quallity of this lens is truly outstanding.